The present invention relates to the field of two and four stroke engine and carburetor tuning. More particularly, the present invention relates to an improved bowl-type carburetor which permits the control of the amount of fuel that passes through a main jet thereof to adjust carburation.
In a two-stroke engine, the air to fuel ratio is critical to the engine""s performance and must be mixed in proper proportions by weight. It is the function of the carburetor to supply the proper mixture to the engine under all operating conditions. If there is excess fuel, the engine will run rich and lose horsepower. Carbon deposits are also created which foul the spark plug, adversely affecting the performance of the engine and even shutting off the engine in extreme cases. On the other hand, insufficient fuel will make the engine run lean creating a high temperature condition in the combustion chambers of the engine causing a reduction in horsepower, detonation, possibly pre-ignition and even piston seizing. These problems can turn into expensive engine repairs.
Major functional systems of a carburetor are a float, a float valve mechanism which maintains a constant level of fuel in the bowl, a pilot system that supplies fuel at low speeds, and a main fuel system that supplies fuel at medium and high speeds. In a full throttle position, the main jet orifice determines how much fuel goes into the engine, and therefore its performance. The only way to adjust the mixture of a carburetor coming from the factory is to take the carburetor off the engine, disassemble the plug at the bottom of the bowl, change the main jet, reassemble the carburetor and prime it before its use again.
Typically, on a given race or ride day, the driver of a shifter kart or motorcycle must find the main jet setting that delivers the most power for the weather conditions. Carburation, especially in a two stroke engine, is very sensitive to weather conditions such as barometric pressure, temperature and humidity. Generally, in the morning the driver guesses what the setting of the main jet should be and makes a test run. After returning to the pit area, the spark plug is read to determine if the main jet selection was appropriate. A few trials may be needed to find the appropriate jetting. Even if the carburation was set properly during practice in the morning, if the races are held in the afternoon, the weather conditions may have changed, sometimes drastically. If there is less barometric pressure, the engine will run too rich and have less power. However, if there is an increase in barometric pressure, the engine will run too lean, losing power at first and perhaps seizing later. In either event, the kart or motorcycle will be slowed significantly or even taken out of the race completely due to engine failure.
Accordingly, there is a need for a bowl-type carburetor which can be modified without having to remove and adjust the settings thereof. What is also needed is a bowl-type carburetor which is not limited to pre-determined main jet sizes, but rather is adjustable while driving. The present invention fulfills these needs and provides other related advantages.
The present invention resides in a bowl-type carburetor having a main fuel jet for directing fuel to be mixed with air, which carburation can be adjusted and controlled without the need of disassembling the carburetor and changing the main fuel jet. In accordance with the present invention, this is accomplished by positioning an adjustable orifice plug generally opposite an inlet of an orifice of the main fuel jet. The orifice plug is moved towards and away from the inlet to alter the amount of fuel permitted to flow through the main fuel jet orifice.
Typically, the orifice plug comprises a needle movable into and away from the main fuel jet orifice for altering the amount of fuel permitted to flow therethrough. Preferably, the main fuel jet is modified to include an enlarged orifice for accepting the needle. The means for positioning the needle include threadably inserting the needle through a bowl plug of the carburetor so that the needle is in alignment with the main fuel jet orifice.
The means for moving the needle into and away from the main fuel jet orifice includes a manually actuated worm gear operably associated with an end of the needle extending from the carburetor. A crank block is rotatably connected to an exterior surface of the bowl plug and encases the portion of the worm gear engaged with an end of the needle extending outwardly from the carburetor. To move the needle into and away from the main fuel jet orifice, a rotatable knob, attached to the worm gear generally opposite the crank block, is turned to cause the needle to travel along internal threads of the bowl plug either into or away from the main fuel jet orifice, adjusting the carburation of the engine.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.